fix: update @astrojs/starlight to v0.38.0 for Astro 5.16 compatibility

Fixes dependency conflict where @astrojs/starlight@0.37.x requires
astro@^5.5.0 but package.json specifies astro@^5.16.0.

This resolves npm install failures that prevented fs-extra and other
dependencies from being installed during BMAD installation.

Related issue: Installer errors in v6.0.0-Beta.2

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

package.json

@@ -88,7 +88,7 @@
   },
   "devDependencies": {
     "@astrojs/sitemap": "^3.6.0",
-    "@astrojs/starlight": "^0.37.0",
+    "@astrojs/starlight": "^0.38.0",
     "@eslint/js": "^9.33.0",
     "archiver": "^7.0.1",
     "astro": "^5.16.0",